Warmer water and reduced river flows will cause more power disruptions for nuclear and coal-fired power plants in the United States and Europe in future, scientists say, and lead to a rethink on how best to cool power stations in a hotter world.
In a study published on Monday, a team of European and US scientists focused on projections of rising temperatures and lower river levels in summer and how these impacts would affect power plants dependent on river water for cooling.
The authors predict that coal and nuclear power generating capacity between 2031 and 2060 will decrease by between 4 and 16% in the United States and a 6 to 19% decline in Europe due to lack of cooling water.
The likelihood of extreme drops in power generation, either complete or almost-total shutdowns, was projected to almost triple.
"This study suggests that our reliance on thermal cooling is something that we're going to have to revisit," co-author Dennis Lettenmaier, a professor of civil and environmental engineering at the University of Washington in Seattle, said in a statement.
Thermoelectric power plants supply more than 90 percent of electricity in the United States and account for 40% of the nation's freshwater usage, says the study published in the journal Nature Climate Change.
In Europe, such plants supply three-quarters of the electricity and account for about half of the freshwater use.
Coal, nuclear and gas plants turn large amounts of water into steam to spin a turbine. They also rely on water at consistent temperatures to cool the turbines and any spike in river water temperatures can affect a plant's operation.
Disruptions to power supplies were already occurring, the authors noted.
During warm, dry summers in 2003, 2006 and 2009 several power plants in Europe cut production because of restricted availability of cooling water, driving up power prices.
A similar event in 2007-2008 in the United States caused several power plants to reduce production, or shut down for several days because of a lack of water for cooling and environmental restrictions on warm water discharges back into rivers, the study said.
In the past few months, large parts of the United States have suffered record heat, with March being the warmest on record for the contiguous 48 states, according to the National Oceanic and Atmospheric Administration.
The study projects the most significant US impacts at power plants inland along major rivers in the Southeast.